The present invention relates to an apparatus and method for automatically selecting a broadband frequency, more particularly, to an apparatus, method and readable medium capable of automatically selecting a channel of a broadband frequency using approximated frequency mapping function.
A common TV set has to select a desired TV channel automatically and suppress signals that may induce falling of TV quality or difficulties in watching of TV broadcasting. These signals are an interference signal, an image signal, Intermediate Frequency Beat (hereafter, it is called as xe2x80x9cIF Beatxe2x80x9d), and a spurious signal and affect to a TV set like followings.
First, watching of TV broadcasting is impossible by saturation of a low noise amplifier and a mixer at the front end of a tuner due to a large interference signal of adjacent band.
Second, receiving sensitivity of TV is getting worse due to the existence of mutual modulation component by two or more large interference signal of adjacent band in band passed by the TV channel being watched.
Third, receiving sensitivity of TV is decreased by influx of the signal corresponding to an image signal and IF beat component of a receiver or by converting its frequency into an intermediate frequency generated at the receiver comprising a desired TV information.
Several methods are proposed to solve the problems.
FIG. 1 is a block diagram of a tuner for conventional double frequency conversion. The conventional tuner can automatically select TV channel frequency on a receiving route and suppress an image signal, IF Beat, a spurious component by local power without an additional circuit.
However, the tuner has problems when it receives the broadcasting signal from multi-channel simultaneously. Particularly, since the tuner cannot suppress a strong undesired broadcasting interference signal, an operation region of receiver becomes small, and at the worst, a low noise amplifier and a mixer may enter upon a saturation state of a power.
FIG. 2 is a block diagram of a prior NTSC TV tuner. The tuner of FIG. 2 is a present common analogue broadcasting tuner (it use 3 bands) and, as the tuner of FIG. 2, can automatically select a TV channel.
The tuner of FIG. 2 uses a tracking filter instead of a bandpass filter at front end of a receiver. Thus, it can suppress a strong broadcasting interference signal (the signal has a VHF band of 10 MHz or more and an UHF band of 30 MHz or more) and has a broad operation region of a receiver. However, the performance of the receiver is getting worse, because of existence of an image signal and IF Beat component in a band of a desired IF signal by one frequency conversion in receiving multi-channel broadcasting signal.
Nowadays, a common NTSC (National Television Systems Committee) tuner and TV tuner for the digital terrestrial broadcasting (hereafter it is called as xe2x80x9cDTV tunerxe2x80x9d) under developing have to receive a broadcasting input frequency of 50-810 MHz and accommodate all of 181 channels comprising cable TV channels as well as broadcasting channels (CH2-CH69). Also, the tuner must be able to tune a channel frequency automatically with at least interface (for example, automatic gain controller and IIC-Bus terminal). The NTSC is one of methods for color television transmitting used in USA, Korea, Japan, etc.
The NTSC tuner generates a desired signal by one frequency conversion, while the DTV tuner uses double frequency conversion to minimize effect of an image signal and IF Beat.
However, as these tuners divides a broadcasting frequency band into three bands (VHF_L, VHF-h and UHF) or two bands (VHF and UHF) by using a tracking filter at the front end of tuner, it can improve various characteristics(for example, intermodulation, crossmodulation, linearity) invoked by linearity extension of a receiver and out-of-band interference signal.
FIG. 3 is a diagram showing a frequency mapping of a prior NTSC TV tuner and FIG. 4 is a diagram showing a frequency mapping of a prior DTV involving a tracking filter.
Automatic selection function of the NTSC tuner, as described FIG. 3, selects a corresponding frequency band of the routes divided in 2 bands or 3 bands respectively by a band switching operation of a tracking filter, a mixer and a voltage control oscillator and a frequency tuning voltage.
That is, the frequency tuning voltages of the tracking filter, mixer and voltage control oscillator to the each band form one route and operate according to the frequency control voltage of about 0-30V. Thus, the tuner can automatically select frequency by one-to-one mapping between frequency operations according to the tuning voltage of a voltage control oscillator and a tracking filter.
However, the front end of the DTV tuner comprising a tracking filter, as described FIG. 4, selects a frequency of the tracking filter corresponding to only one among the 3bands or 2bands according to the tuning voltage by a switching operation. Namely, unlike the NTSC tuner, since one voltage control oscillator in the DTV tuner comprises all of broadcasting frequency bands (BW=760 MHz) for the frequency tuning voltage by phase synchronization loop, the frequency mapping between a tracking filter and voltage control oscillator for a frequency tuning voltage cannot be performed. At results, the prior tuner cannot perform an automatic selection of frequency.
The object of the present invention is to provide an apparatus, method and readable medium capable of automatically selecting a broadband frequency channel using approximated frequency mapping function.
The another object of the present invention is to provide an apparatus, method and readable medium capable of automatically selecting a broadband frequency channel by calibrating a frequency in even of change of the characteristics of tuning frequency.
In accordance with the object of the present invention, there is provided an apparatus for automatic selection of a broadband frequency channel using double frequency conversion comprising: a frequency band dividing part for dividing a desired receiving frequency into a classified band according to a tuning voltage; a frequency converting part for performing double frequency conversion converting the divided frequency into an intermediate frequency of a desired band; a first controlling part for controlling the double frequency conversion of the frequency converting part; and a second controlling part for selecting a coefficient of an approximated frequency mapping function for a channel corresponding to a channel conversion selection signal from outside from previously stored coefficients of approximated frequency mapping function for the divided frequency.
Also, in accordance with another object of the present invention, there is provided a method for automatic selection of a broadband frequency channel using double frequency conversion comprising the steps of: a first step for finding and storing a coefficient of approximated frequency mapping function for a divided frequency by using the divided frequency characteristic and the approximated frequency mapping function, wherein the divided frequency is divided according to a tuning voltage; a second step for receiving a channel conversion signal from outside and for selecting a coefficient of approximated frequency mapping function for the channel from the stored coefficients of approximated frequency mapping function for the divided frequency; and a third step for finding a tuning voltage by using the coefficient selected at the second step and for converting a channel according to the tuning voltage.
Also, in accordance with another object of the present invention, there is provided a medium read by a computer, in which is recorded with a program for implementing functions in an apparatus for automatic selection of broadband frequency channel including a processor, the functions comprising: a first function for finding and storing a coefficient of approximated frequency mapping function for a divided frequency by using the divided frequency characteristic and the approximated frequency mapping function, wherein the divided frequency is divided according to a tuning voltage; a second function for receiving a channel conversion signal from outside and for selecting a coefficient of approximated frequency mapping function for the channel from the stored coefficients of approximated frequency mapping function for the divided frequency; and a third function for finding a tuning voltage by using the selected coefficient and for converting a channel according to the tuning voltage.